Although based on research, with dialogue that scavenges Ernest Hemingway and Martha Gellhorn's writings, this HBO biopic is never quite believable.

HBO's two-for-one biopic "Hemingway & Gellhorn," which would more appropriately reverse the order of those names, dramatizes the stormy coming together and falling apart of the famous novelist and his third wife, war correspondent Martha Gellhorn. The film, which premieres Monday, is a big-name affair, with Clive Owen and Nicole Kidman in the leads and Philip Kaufman directing a screenplay by Barbara Turner ("Pollock") and Jerry Stahl ("Bad Boys II").

But — though it is clearly based on research, with dialogue that scavenges the principals' own writing — it is never quite believable, either as history or drama.

To be sure, it's impossible to re-create with any accuracy any actual person, and biopics (even as long a one as this) are typically deformed by the need to cover a lot of ground in short order: As one crisis follows quickly upon another, characters can seem both abnormally intense and insufficiently motivated. Kidman benefits from Gellhorn's relative obscurity in creating her, of course; the original person matters less. And yet given the unknowability of even as public a figure as Hemingway, there are as many plausible ways to play him as to play Hamlet. One doesn't need to feel that, yes, it was really like this, only that it might have been.

Still, from the moment young writer Martha, 28, sidles up to the celebrated Ernest, a decade older and covered in marlin blood, at a Key West bar, we never really lose the sense that we're in a movie, in the company of play actors, not of people.

"Friend or foe?" asks Hemingway.

"Or faux friend. You never know," answers Gellhorn, who might be Lauren Bacall teaching Humphrey Bogart to whistle. (Or Marion Ravenwood saying, "Indiana Jones. I always knew some day you'd come walking back through my door," in a movie whose story Kaufman co-wrote.)

And they're off, from Florida to the Spanish Civil War to Cuba and China and D-day, as competitors and collaborators. They meet other famous faces (the starry supporting cast includes David Strathairn as a rather too pathetic John Dos Passos and Metallica drummer Lars Ulrich, really, as documentary filmmaker Joris Ivens); enact passages from future memoirs and biographies rejiggered for dramatic effect; dodge bullets and down cocktails: "You're more of a man than most men I've met," he says admiringly, as he fails to drink her under the table.

Kaufman, who also directed the erotic period pieces "The Unbearable Lightness of Being" and "Henry & June," would seem a natural choice here, and although the film begins with Gellhorn's disclaimer that she was "probably the worst bed partner on five continents," he puts a lot of energy into sex scenes that make her disclaimer read like false modesty. (Granted, all do not involve a bed; in one that does, bombs rain down on their Madrid hotel, covering their naked movie-star bodies in plaster dust.)

Interestingly, the most engaging aspect of "Hemingway & Gellhorn" is its most boldly artificial. Shot entirely in and around San Francisco, the film hides its budget — modest for an international mini-epic of war and romance — by integrating the actors "Zelig" style into old newsreel footage, sliding from color into monochrome and back again. Sometimes, you don't notice the trick at all, but even when you do, it can be sort of charming: It gives the film a kind of picture-book quality not out of step with its self-dramatizing subjects.

The returns in their relationship eventually diminish: The student outlives her need for the teacher, who derides her as "Little Miss Human Interest." It turns out that he's the conventional one who needs a base and a gang; she's the footloose free spirit who wants to be where the action is. References to castration increase. (She has his cats neutered, but, as she points out, they were spraying all her clothes.)

Gellhorn seems increasingly engaged — "Innocent people are being blown up," she declares before decamping for Finland. "Someone has to write about this" — even as Hemingway grows clownish, petty and belligerent: "They'll be reading my stuff long after the worms have finished with you," he yells after her.

The movie, which has concentrated more on her journey than his, gives her a kind of payback: It jumps from their final breakup, in 1945, to a diminished Hemingway's suicide some 16 years later. Gellhorn exits on two feet, as the older woman who has remembered this tale, grabbing her backpack and heading out the door.